Technical Field
The invention relates to a power conversion technique. Particularly, the invention relates to an inverter and a power supplying method thereof and an application using the same.
Related Art
In a design of an inverter, an auxiliary circuit thereof (for example, a control portion, a driving portion or a communication portion) generally requires different isolated voltages (for example, 12V, 5V) to serve as power supplies. It is meaningful for ensuring a high efficiency and stable operation of the inverter by designing a reliable auxiliary power supply with a simple structure to supply the auxiliary power to the auxiliary circuit.
In an existing technique, a flyback converter is generally used to serve as a power supplying circuit for providing the auxiliary power. However, in some applications of the inverter, using the flyback converter to supply the auxiliary power to the inverter may cause unexpected power waste. For example, when the inverter is applied to a photovoltaic grid-connected system (the inverter is referred as a photovoltaic inverter), since a direct current (DC) input voltage of the photovoltaic inverter is an output of a photovoltaic module, and the output of the photovoltaic module relates to an intensity of the sunlight, a magnitude of the DC input voltage actually received by the photovoltaic inverter is varied along with time, thus the photovoltaic inverter is not maintained to operate under a rated power. In detail, most of the operational time of the photovoltaic inverter is working under a light load state, so that the actual power conversion efficiency of the photovoltaic inverter is not only evaluated according to the power conversion efficiency under the rated power, but also required to satisfy a demand of European efficiency (i.e. a power conversion efficiency calculated by accumulating different loads according to different weights).
Due to a high voltage stress of the flyback converter and a feature of hard switching, the power conversion efficiency of the inverter working under the light load state is low. As a result, it is hard to enhance the European efficiency of the photovoltaic inverter adopting the flyback converter as the auxiliary power circuit.